Downhole tool frequently involve mechanisms to hold one portion of the tool to another. This is sometimes accomplished using shearable members such as shear pins or similar devices such as spring loaded collets. Typically pistons are used with such locking elements to respond to built up pressure after landing a ball on a seat and adding pressure from above. Some of the problems with these designs lead to premature failure of the locking device creating a problem downhole. If the tool is a disconnect, for example, it may release prematurely forcing a fishing operation to retrieve the lowermost portion that falls in the wellbore. One of the reasons for the premature failure of the shear pins is the weight of the piston that has to ultimately move to break the shear pin or release a collet. Due to cyclical loading during run in or from operation of adjacent downhole equipment such as downhole pumps the shock loads on the piston combined with its weight can be sufficient to shear a pin or otherwise allow relative movement of tool components at an inopportune time.
Other limitations of prior designs is that the locking members that were used to hold the components fixed to each other provided only discrete areas of contact about the periphery of the components causing elevated stress levels due to the minimal contact areas and creating another weakness that has in the past lead to premature failure.
What is needed is a design to eliminate these premature failures with a design that does not become even more complex than the prior designs sought to be upgraded. The present invention offers solutions that meet this need. The shear pin or collet designs that were prone to failure in the past have been eliminated. In an embodiment of the invention locking components offer as much as 360 degree support to minimize shear failure. Unlocking is accomplished by radial movement of the locking members to release the grip between the members initially held together. Once the release is accomplished a lockout feature can be provided to prevent re-engagement. Radial movement can be accomplished in a variety of ways with pistons or a sleeve that bends responsive to applied internal pressure or by other mechanisms. The design that provides as much as full circumferential contact prior to unlocking can also take on a variety of forms. The application can be for a host of downhole tools although aspects of the preferred embodiment will be described in the context of a hydraulic release tool.
The prior art release tools that suffered from the limitations described above are represented by the following list of U.S. patents, presented as some examples of the issues affecting the prior art designs of hydraulic disconnects: U.S. Pat. Nos. 5,526,888; 6,527,048; 6,439,305; 6,408,946; 6,349,767; 6,318,470; 6,053,262; 6,053,250; 5,984,029; 5,960,884; 5,787,982; 5,718,291 and 4,984,632. Also of interest is U.S. Application 2004/0045704.
Those skilled in the art will appreciate the varied applications of the present invention and its advantages from a detailed discussion of two embodiments and the claims, which appear below.